Watching billions of leaves turn from green to auburn is one of nature’s most beautiful annual shows. When days begin to grow shorter, deciduous (green leafy) trees start signaling their leaves to stop producing chlorophyll, the green pigment responsible for the leaves’ color and photosynthesis.
Because the color change is more dependent on light than temperature, it takes place at basically the same time year after year, says the US National Arboretum.
But there are exceptions to this rule, as we’re witnessing this year. Temperature and weather conditions, can, impact the intensity of fall colors and how long they linger. They can also subtly affect the timing of when the leaves start to change. And drought can change the rate at which the leaves turn, as Scientific American explains:
So in the Boston area and central Massachusetts, where drought is severest in the Northeast, fall colors have likely come earlier, with more trees with brown leaves. While in the North Carolina Appalachians, more moderate drought levels—along with warmer temperatures—delayed the peak by about a week or more.
The reasons why drought can influence the autumn colors aren’t well understood, but “seem to be related to a slow-down in the metabolic processes of the trees when they are under only mild water stress, vs. the shutdown that comes from more intense pressure,” Scientific American reports.
The good news: That means for many people, especially in the Mid Atlantic, there’s still time to catch the show.
The website The Foliage Network shows that much of the Mid-Atlantic and South East have not peaked yet.
Maryland’s latest fall foliage report (from October 28) shows that much of the state has yet to reach peak color.
Though in most of the Northeast, the show’s over.
And Weather.com shows there’s some foliage to be seen in the Mid West, but it’s currently peaking and may fade quick.
In any case, by mid November all the leaves will likely have peaked across the country.
Why do the leaves turn red, orange, or yellow?
When the chlorophyll disappears, the arboretum explains, other chemicals in the leaves persist and show their colors:
Chlorophyll normally masks the yellow pigments known as xanthophylls and the orange pigments called carotenoids — both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season. Red and purple pigments come from anthocyanins. In the fall anthocyanins are manufactured from the sugars that are trapped in the leaf. In most plants anthocyanins are typically not present during the growing season.
Different trees will reveal different colors, as the US Forest Service describes on its website. The leaves of oak trees, for example, turn reddish brown or russet. Here are a few others:
- Hickories: golden bronze
- Aspen and yellow-poplar: golden yellow
- Dogwood: purplish red
- Beech: light tan
- Sourwood and black tupelo: crimson
The color of maples leaves differ species by species:
- Red maple: brilliant scarlet
- Sugar maple: orange-red
- Black maple: glowing yellow
- Striped maple: almost colorless
How do I see the trees?
It’s easy: Go outside!